Close planting of dwarf varieties is currently the main cultivation direction for pear trees, and the screening of excellent dwarf varieties is an important goal for breeders.  In this study, the dwarfing pear variety ‘601D’ and its vigorous mutant ‘601T’ were used to show their biological characteristics and further explore the dwarfing mechanism in ‘601D’.  The biological characteristics showed that ‘601D’ had a shorter internode length, a shorter and more compact tree body, thicker and broader leaves, lower stomata density, larger stomata size (dimension), and higher photosynthetic capacity.  The biological characteristics of ‘601T’ showed notable contrasts.  The results of endogenous hormone tests indicated that the contents of abscisic acid (ABA), ABA-glucosyl ester, and GA4 were higher in ‘601D’, but the trans-zeatin content was lower.  By transcriptomic analysis, significant differences were found in the biosynthetic and metabolic pathways of ABA.  Related transcription factors such as bHLH, WRKY, and homeobox also participated in the regulation of plant dwarfing.  We therefore examined three hormones with obvious differences with ‘601T’, and found that only ABA could induce ‘601T’ to return to a dwarfing plant phenotype.  Therefore, we conclude that the dwarfing of ‘601D’ is caused by an excessive accumulation of ABA.  This study provides a new theoretical basis for breeding dwarf varieties.

Citrus canker, an epidemic quarantine disease caused by Xanthomonas axonopodis pv. citri, has brought a great damage in citrus production worldwide. Herein, a rice PRR (pattern recognition receptor) gene Xa21 together with GUS reporter gene and hygromycin phosphotransferase gene (HPT) was introduced into Anliucheng sweet orange (Citrus sinensis Osbeck) via Agrobacterium-mediated transformation of embryogenic callus. The transgenic calluses were screened on MT basal medium containing hygromycin (HYG) and detected by histochemical GUS staining. The transgenic plantlets were recovered through somatic embryogenesis pathway. The regenerated plantlets were accustomed to and maintained in the greenhouse. The transgene integration of recovered plantlets was identified by PCR and Southern blot hybridization. It showed that all the transgenic plantlets tested had undergone single copy integration, the expression of Xa21 in eight different transgenic lines detected by qRT-PCR can be divided into three grades, high for T5 and T6, middle for T4 and low for the rest. The tolerance to citrus canker disease of the three recovered transgenic lines T2, T4 and T6 was assessed by in vitro pin-puncture inoculation. The results showed that all the three transgenic lines conferred improved resistance to citrus canker bacterium infection and the T4 transgenic line displayed the highest resistance. The mechanism and feasibility of rice Xa21 in triggering innate immunity in citrus was briefly discussed.